LCD devices are widely used in flat panel displays for monitors, televisions and/or other displays. As is well known to those having skill in the art, an LCD display generally includes a planar array of LCD devices that act as an array of optical shutters. Transmissive LCD displays employ backlighting using fluorescent cold cathode tubes above, beside and sometimes behind the array of LCD devices. A diffusion panel behind the LCD devices can be used to redirect and scatter the light evenly to provide a more uniform display.
For example, it is known to use one or more fluorescent cold cathode tubes adjacent one or more edges of the planar array of LCD devices, and a light guide or light pipe that directs the light from the fluorescent cold cathode tubes, to illuminate the face of the planar array of LCD devices. Unfortunately, such edge lighting may be inefficient, with up to 50% or more of the light being lost.
It is also known to provide an array of fluorescent cold cathode tubes behind and facing the planar array of LCD devices. Unfortunately, an array of fluorescent cold cathode tubes may increase the thickness of the LCD display and/or increase the power consumption thereof. It also may be difficult to uniformly illuminate the planar array of LCD devices with the array of fluorescent cold cathode tubes.
Semiconductor light emitting devices, such as Light Emitting Diode (LED) devices, also may be used for edge illumination of a planar array of LCD devices. For example, U.S. patent application Ser. No. 10/898,608, filed Jul. 23, 2004, entitled Reflective Optical Elements for Semiconductor Light Emitting Devices, to coinventor Negley, and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes side emission LEDs that may be used for large area LCD and/or television backlighting.
Semiconductor light emitting devices, such as LED devices, also may be used for direct backlighting of LCD displays. For example, U.S. patent application Ser. No. 11/022,332, filed Dec. 23, 2004, entitled Light Emitting Diode Arrays For Direct Backlighting Of Liquid Crystal Displays, to coinventor Negley et al., and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference in it entirety as if set forth fully herein, describes an array of LED devices that is closely spaced apart from an array of LCD devices to provide backlighting therefor.
It is generally desirable to provide backlighting for an LCD display that appears uniform to a user of the display. Uniform backlighting may be provided by increasing the space between the LED devices or cold cathode tubes and the diffusion panel, to allow a relatively thick “mixing zone”, wherein the light output from the LED devices and/or fluorescent tubes can mix uniformly. Unfortunately, if the thickness of the mixing zone is increased, the overall thickness of the flat panel display may also undesirably increase. Backlighting uniformity also may be provided by decreasing the pitch between adjacent LED devices and/or fluorescent cold cathode tubes. Unfortunately, if the pitch is decreased, more LED devices and/or fluorescent cold cathode tubes may be used, which may undesirably increase the cost and/or power consumption of the flat panel display.